New Process

ABSTRACT

The present invention relates to a process for the preparation of S-[2-[1-(2-ethylbutyl)cyclohexylcarbonylamino]-phenyl] 2-methylthiopropionate which is useful as a pharmaceutically active compound.

PRIORITY TO RELATED APPLICATION(S)

This application claims the benefit of European Patent Application No. 10195294.3, filed Dec. 16, 2010, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

S-[2-([[1-(2-ethylbutyl)cyclohexyl]carbonyl]amino) phenyl] 2-methylpropanethioate has been shown to be an inhibitor of CETP activity in humans (de Grooth et al., Circulation, 105, 2159-2165 (2002)) and rabbits (Shinkai et al., J. Med. Chem., 43, 3566-3572 (2000); Kobayashi et al., Atherosclerosis, 162, 131-135 (2002); and Okamoto et al., Nature, 406 (13), 203-207 (2000)). S-[2-([[1-(2-ethylbutyl)cyclohexyl]carbonyl]amino) phenyl] 2-methylpropanethioate has been shown to increase plasma HDL cholesterol in humans (de Grooth et al., supra) and in rabbits (Shinkai et al., supra; Kobayashi et al., supra; Okamoto et al., supra). Moreover, S-[2-([[1-(2-ethylbutyl)cyclohexyl]carbonyl]amino) phenyl] 2-methylpropanethioate has been shown to decrease LDL cholesterol in humans (de Grooth et al., supra) and rabbits (Okamoto et al., supra). Additionally, S-[2-([[1-(2-ethylbutyl)cyclohexyl]carbonyl]amino)phenyl] 2-methylpropanethioate inhibits the progression of atherosclerosis in rabbits (Okamoto et al., supra).

SUMMARY OF THE INVENTION

The present invention relates to a process for the preparation of S-[2-[1-(2-ethylbutyl)cyclohexylcarbonylamino]-phenyl] 2-methylthiopropionate which is useful as a pharmaceutically active compound.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise stated, the following terms used in the specification and claims have the meanings given below:

The term “halo” or “halide” means fluoro, chloro, bromo or iodo. In particular embodiments, the halo is chloro or bromo.

The term “(C₁-C₈)alkyl” refers to a branched or straight hydrocarbon chain of one to eight carbon atoms. Examples include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, ethyl-butyl, pentyl, hexyl, heptyl and octyl.

The term “(C₁-C₈)alkoxy” means a moiety of the formula —OR^(ab), wherein R^(ab) is a (C₁-C₈)alkyl moiety as defined herein. Examples of alkoxy moieties include, but are not limited to, methoxy, ethoxy, isopropoxy, and the like.

The term “(C₃-C₈)cycloalkyl” refers to a single saturated carbocyclic ring of thee to eight ring carbons. Examples include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. The (C₃-C₈)cycloalkyl may optionally be substituted with one or more substituents, preferably one, two or three, substituents. Preferably, the (C₃-C₈)cycloalkyl substituent is selected from the group consisting of a (C₁-C₈)alkyl, hydroxy, (C₁-C₈)alkoxy, halo(C₁-C₈)alkyl, halo(C₁-C₈)alkoxy, halo, amino, mono- and di-(C₁-C₈)alkylamino, hetero(C₁-C₈)alkyl, acyl, aryl and heteroaryl.

The term “aryl” means a monovalent monocyclic or bicyclic aromatic hydrocarbon moiety which is optionally substituted with one or more substituents. Preferably, the aryl is substituted with one, two or three substituents, each of which is preferably selected from the group consisting of a (C₁-C₈)alkyl, hydroxy, (C₁-C₈)alkoxy, amino, mono- and di-(C₁-C₈)alkylamino, carboxy, (C₁-C₈)alkylsulfonyl, —SO₂-aryl, —SO₃H, —SO₃—(C₁-C₈)alkyl or —SO₂—NR^(ac) ₂, wherein each R^(ac) is independently hydrogen or a (C₁-C₈)alkyl. More specifically the term aryl includes, but is not limited to, phenyl, 1-naphthyl, 2-naphthyl, and the like, each of which can be substituted or unsubstituted.

The term “heteroaryl” means a monovalent monocyclic or bicyclic moiety of 5 to 12 ring atoms having at least one aromatic ring containing one, two, or three ring heteroatoms selected from N, O, or S with the remaining ring atoms being carbon, with the understanding that the attachment point of the heteroaryl moiety will be on an aromatic ring. Preferably, the ring heteroatoms are N or O. The heteroaryl ring can be optionally substituted independently with one or more substituents, preferably one, two or three substituents, each of which is independently selected from a (C₁-C₈)alkyl, halo(C₁-C₈)alkyl, hydroxy, (C₁-C₈)alkoxy, halo, nitro and cyano. More specifically the term heteroaryl includes, but is not limited to, pyridyl, furanyl, thienyl, thiazolyl, isothiazolyl, triazolyl, imidazolyl, isoxazolyl, pyrrolyl, pyrazolyl, pyrimidinyl, benzofuranyl, tetrahydrobenzofuranyl, isobenzofuranyl, benzothiazolyl, benzoisothiazolyl, benzotriazolyl, indolyl, isoindolyl, benzoxazolyl, quinolyl, tetrahydroquinolinyl, isoquinolyl, benzimidazolyl, benzisoxazolyl or benzothienyl, imidazo[1,2-a]-pyridinyl, imidazo[2,1-b]thiazolyl, and the derivatives thereof.

The term “heterogeneous transition metal hydrogenation catalyst” refers to a transition metal hydrogenation catalyst which acts in a different phase than the substrate. Preferably, the heterogeneous transition metal hydrogenation catalyst is in the solid phase. In particular, while the heterogeneous transition metal hydrogenation catalyst is in the solid phase the reactants are in the liquid phase. The heterogeneous transition metal hydrogenation catalyst contains a transition metal which forms one or more stable ions which have incompletely filled d orbitals (i.e. Pd, Pt, Rh, Au, Ni, Co, Ru, Ir) in a particular noble metal, such as Pd, Pt, Rh or Au. In these catalysts the transition metal is in particular “supported”, which means that the catalyst is dispersed on a second material that enhances the effectiveness. The “support” can be merely a surface on which the metal is spread to increase the surface area. The supports are porous materials with a high surface area, most commonly alumina or various kinds of carbon. Further examples of supports include, but are not limited to, silicon dioxide, titanium dioxide, calcium carbonate, barium sulfate, diatomaceous earth and clay. The metal itself can also act as a support, if no other support is present. More specifically, the term “heterogeneous transition metal hydrogenation catalyst” includes but is not limited to, a Raney catalyst (e.g. Ra—Ni, Ra—Co,) Pd/C, Pd(OH)₂/C, Au/TiO₂, Rh/C, Ru/Al₂O₃, Ir/CaCO₃, or Pt/C. In a particular embodiment, the “heterogeneous transition metal hydrogenation catalyst” is not pre-treated with sulphide.

The term “area %” for a substance A refers to the (area of substance A)/(sum of areas of all peaks)×100, area as obtained from HPLC or GC analysis.

In particular embodiments, the chemical groups whose definitions are given above are those specifically exemplified in the examples.

Unless otherwise stated, all percentages are given in weight percent of the total weight of the compound of formula (I).

In a first embodiment, the invention provides a process for the preparation of a compound of formula (I″):

wherein X¹, X², X³ and X⁴ are each independently hydrogen, (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or two adjacent substituents (i.e. X¹ and X² or X² and X³ or X³ and X⁴) together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH, and S wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; R^(a), R^(b), RE and R^(d) are independently a (C₁-C₈)alkyl, a (C₃-C₈)cycloalkyl, aryl or heteroaryl; each R^(e) is independently hydrogen, a (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′), X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or two adjacent substituents (i.e. X^(1′) and X^(2′) or X^(2′) and X^(3′) or X^(3′) and X^(4′)) together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH, and S wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined above, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

Common reduction disulfide processes result inter alia to similar disadvantages. They use reducing agents in stoichiometric amounts leading to safety issues, large amounts of waste and/or laborious work-up. Although these disadvantages on lab scale may not be seen of great importance, when going on large production scale they are looked at carefully due their factorial impact.

The S—S disulfide bonds (and the S—H bonds formed during the hydrogenation) are considered as catalyst poisons, due to the strong chemisorptions of sulfur-containing molecules on metal surfaces (Houben-Weyl, Methoden der Organischen Chemie, Band IV/1c, published 1980, page 486; or F. Zymalkowski, Katalytische Hydrierungen im Organisch-Chemischen Laboratorium, F. Enke Verlag Stuttgart, published 1965, page 37). Therefore, it was surprisingly found that the reduction of a disulfide bond according to the present invention is selective with high throughput.

The present invention does not require a pretreatment of the catalyst, in particular, there is no need of sulfide pretreatment of the catalysts.

In a second embodiment, the invention provides a process for the preparation of a compound of formula (I′″):

wherein X¹, X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or two adjacent substituents (i.e. X¹ and X² or X² and X³ or X³ and X⁴) together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH, and S wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; R¹ is a (C₁-C₈)alkyl or aryl; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, (C₃-C₈)cycloalkyl, aryl or heteroaryl; each R^(e) is independently hydrogen, (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

-   -   wherein X^(1′), X^(2′), X^(3′) and X^(4′) are each independently         hydrogen, (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a),         —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or         two adjacent substituents (i.e. X^(1′) and X^(2′) or X^(2′) and         X^(3′) or X^(3′) and X^(4′)) together with the carbon atoms to         which they are attached form a four, five or six membered         cycloalkyl ring that optionally includes an additional         heteroatom selected from the group consisting of O, NH and S,         wherein the four, five or six membered cycloalkyl ring is         optionally substituted with one to three substituents         independently selected from the group consisting of a         (C₁-C₈)alkyl and aryl; and R^(a), R^(b), R^(c), R^(d), R^(e),         X¹, X², X³ and X⁴ are as defined above,         with H₂ in the presence of an acylating agent such as an         anhydride derivative [((C₁-C₈)alkyl)C(═O)]₂O or [aryl(C═O)]₂O or         a halide derivative ((C₁-C₈)alkyl)C(═O)halide or aryl(C═O)halide         and a heterogeneous transition metal hydrogenation catalyst.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (I″):

wherein X¹ is —NH—C(═O)R^(d), wherein R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl, in particular R^(d) is (2-Ethyl-butyl)-cyclohexyl; X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂, in particular X², X³ and X⁴ are each independently hydrogen or a (C₁-C₈)alkyl; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, a (C₃-C₈)cycloalkyl, aryl or heteroaryl; each R^(e) is independently hydrogen, a (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′) is —NH—C(═O)R^(d) or —NR^(e) ₂; R^(d) is a (C₁-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl, in particular embodiments R^(d) is (2-Ethyl-butyl)-cyclohexyl; R^(e′) is hydrogen; X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(e), —NH—C(═O)R^(d) or —NR^(e) ₂, in particular embodiments X^(2′), X^(3′) and X^(4′) are each independently hydrogen or a (C₁-C₈)alkyl; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined above, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (I′″):

wherein X¹ is —NH—C(═O)R^(d), wherein R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl, in particular embodiments R^(d) is (2-Ethyl-butyl)-cyclohexyl; X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(—O)R^(d) or —NR^(e) ₂, in particular embodiments X², X³ and X⁴ are each independently hydrogen or (C₁-C₈)alkyl; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, a (C₁-C₈)cycloalkyl, aryl or heteroaryl; each R^(e) is independently hydrogen, a (C₁-C₈)alkyl or aryl; R¹ is a (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′) is —NH—C(═O)R^(d) or —NR^(e′) ₂; R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl, in particular embodiments R^(d) is (2-ethyl-butyl)-cyclohexyl; R^(e′) is hydrogen; X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂, in particular embodiments X^(2′), X^(3′) and X^(4′) are each independently hydrogen or (C₁-C₈)alkyl; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined above, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In a further embodiment the present invention provides a process for the preparation of compound of formula (I′):

which comprises reacting a compound of formula (II′):

wherein R is H or with a compound of the formula

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In a further embodiment the present invention provides a process for the preparation of the compounds of formula (I′) and Formula (X):

which comprises reacting a compound of formula (II′):

wherein R is H or with a compound of the formula

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In another embodiment, the present invention provides a process for the preparation of compounds of formula (I′) and Formula (X):

which comprises reacting a compound of formula (II):

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In another embodiment the present invention provides a process for the preparation of a compound of formula (I′):

which comprises reacting a compound of formula (II):

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (Ia):

wherein R¹ is a (C₁-C₈)alkyl or aryl, in particular R¹ is isopropyl, which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of an acylating agent such as an anhydride derivative [((C₁-C₈)alkyl)C(═O)]₂O or [aryl(C═O)]₂O or a halide derivative ((C₁-C₈)alkyl)C(═O)halide or aryl(C═O)halide and a heterogeneous transition metal hydrogenation catalyst. In particular, when R¹ is isopropyl, the acylating agent is isobutyric anhydride or isobutyryl halide, in particular isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of compounds of formula (Ia) and Formula (X):

wherein R¹ is a (C₁-C₈)alkyl or aryl, and in particular embodiments R¹ is isopropyl, which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of an acylating agent such as an anhydride derivative [((C₁-C₈)alkyl)C(═O)]₂O or [aryl(C═O)]₂O or a halide derivative ((C₁-C₈)alkyl)C(═O)halide or aryl(C═O)halide and a heterogeneous transition metal hydrogenation catalyst. In particular, when R¹ is isopropyl, the acylating agent is isobutyric anhydride or isobutyryl halide, in particular isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (I):

which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of acylating agent such as isobutyric anhydride or isobutyryl halide, and more particularly the acylating agent is isobutyric anhydride. In another embodiment, the present invention provides a process for the preparation of compounds of formula (I) and Formula (X):

which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of acylating agent such as isobutyric anhydride or isobutyryl halide, and more particularly the acylating agent is isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (Ia):

wherein R¹ is a (C₁-C₈)alkyl or aryl, and in particular embodiments R¹ is isopropyl, which comprises reacting a compound of formula (II):

with H₂ in the presence of an acylating agent such as an anhydride derivative [((C₁-C₈)alkyl)C(═O)]₂O or [aryl(C═O)]₂O or a halide derivative ((C₁-C₈)alkyl)C(═O)halide or aryl(C═O)halide and a heterogeneous transition metal hydrogenation catalyst. In particular, when R¹ is isopropyl, the acylating agent is isobutyric anhydride or isobutyryl halide, and in particular isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of the compounds of formula (Ia) and Formula (X):

wherein R¹ is a (C₁-C₈)alkyl or aryl, and in particular embodiments R¹ is isopropyl, which comprises reacting a compound of formula (II):

with H₂ in the presence of an acylating agent such as an anhydride derivative [((C₁-C₈)alkyl)C(═O)]₂O or [aryl(C═O)]₂O or a halide derivative ((C₁-C₈)alkyl)C(═O)halide or aryl(C═O)halide and a heterogeneous transition metal hydrogenation catalyst. In particular embodiments, when R¹ is isopropyl, the acylating agent is isobutyric anhydride or isobutyryl halide, and in particular embodiments isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of a compound of formula (I):

which comprises reacting a compound of formula (II):

with H₂ in the presence of an acylating agent such as isobutyric anhydride or isobutyryl halide, and in particular embodiments isobutyric anhydride.

In another embodiment, the present invention provides a process for the preparation of compounds of formula (I) and Formula (X):

which comprises reacting a compound of formula (II):

with H₂ in the presence of acylating agent such as isobutyric anhydride or isobutyryl halide, and in particular embodiments isobutyric anhydride.

In particular embodiments, the present invention provides a process for the preparation of S-[2-([[1-(2-ethylbutyl)-cyclohexyl]-carbonyl]amino)phenyl]2-methylpropanethioate comprising the formation of a compound of formula (I′):

which comprises reacting a compound of formula (II):

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.

The present invention as described above may be carried out in the presence of a solvent or a mixture of two or more solvents. In particular the solvent is an organic solvent such as an ether like solvent (e.g. tetrahydrofuran, methyltetrahydrofuran, diisopropyl ether, t-butylmethyl ether or dibutyl ether), ester like solvent (e.g. ethyl acetate, isopropyl acetate butyl acetate), aliphatic hydrocarbon solvent (e.g. hexane, heptane or pentane), saturated alicyclic hydrocarbon solvent (e.g. cyclohexane or cyclopentane), or aromatic solvent (e.g. toluene, o-m- or p-xylene or t-butyl-benzene), or a mixture thereof. In particular, the hydrogenation step according to the present invention is carried out in the presence of a solvent selected from an ether like solvent, ester like solvent, aliphatic hydrocarbon solvent, saturated alicyclic hydrocarbon solvent, aromatic solvent, and mixtures thereof, when no acylating agent is present; and in particular embodiments the solvent is an aliphatic hydrocarbon solvent, saturated alicyclic hydrocarbon solvent or aromatic solvent.

In another embodiment the anhydride derivative can act as a solvent or co-solvent, e.g. molar ratio anhydride/amidodisulfide of 2 to 20, and in particular 2 to 5.

In a particular embodiment, the present invention provides a process as described above, wherein the acylating agent is isobutyric anhydride. In particular embodiments, 2.0 to 4.0 equivalents of isobutyric anhydride with respect to the disulfide of formula (II) are used. More particularly, 2.5 to 3.5 equivalents are used.

In a particular embodiment, the present invention provides a process as described above wherein the reaction is carried out at temperature up to 150° C., in particular between 25° C. and 150° C., more particularly between 60° C. to 90° C., most particularly at 80° C.

In a particular embodiment, the present invention provides a process as described above wherein the H₂ is added at a pressure of at least 0.1 bar, particularly at a pressure between 0.1 to 100 bar, more particularly at a pressure between 0.2 bar to 30 bar, most particularly 5 to 25 bar.

In a particular embodiment, the present invention provides a process as described above wherein the heterogeneous transition metal hydrogenation catalyst is a Raney catalyst, Pd/C, Pd(OH)₂/C, Nanoparticulate Palladium(0) microencapsulated in polyurea matrix (NP Pd(0) Encat™ 30), Au/TiO₂, Rh/C, Ru/Al₂O₃, Ir/CaCO₃, or Pt/C, or a mixture thereof, particularly the heterogeneous transition metal hydrogenation catalyst is a Raney catalyst, Pd/C, Pd(OH)₂/C, Au/TiO₂, Rh/C, Ru/Al₂O, Ir/CaCO₃, or Pt/C, or a mixture thereof, more particularly the heterogeneous transition metal hydrogenation catalyst is Pd/C, Pd(OH)₂/C, Au/TiO₂, Rh/C, Ra—Ni or Pt/C, and most particularly the heterogeneous transition metal hydrogenation catalyst is Pd/C or Ra—Ni. The hydrogenation can be run in the presence of a molar excess of palladium towards the disulfide. More conveniently, palladium is used in catalytic amounts, e.g. 0.001 to 0.1 equivalents, preferably 0.01 to 0.1 equivalents with respect to the disulfide. The catalyst can be re-used several times such that the ratio between the disulfide converted and the moles of palladium employed is increased correspondently.

In another embodiment, the present invention provides a compound of formula (X):

In another embodiment the present invention provides a composition comprising a compound of formula (I):

and comprising a compound of formula (X):

and having less than 0.1% of the compound of formula (X) by weight.

In another embodiment, the present invention provides a composition comprising a compound of formula (I):

and comprising a compound of formula (X):

and having between 1 ppb (parts per billion in weight) and 100 ppm (parts per million in weight) of the compound of formula (X), and in particular embodiments having between 1 ppb and 1 ppm of the compound of formula (X).

Compounds of formulae (I′) and (X) can be prepared according to scheme 1 wherein the process conditions are herein described:

Compounds of formulae (I) and (X) can be prepared according to scheme 2 wherein the process conditions are herein described:

Compounds of formulae (II) and (II′) can be prepared according to scheme 3:

wherein X is I, Br, Cl or F. In particular, the process comprises reacting a cyclohexanecarboxylic acid derivative of formula (IV) with a halogenating agent, such as PX₃, PX₅, SOX₂ or NCX, COX₂ to obtain the acyl halide of formula (III). The halogenating step is preferably carried out in the presence of tri-(C₁-C₈)alkylamine. Furthermore, the process comprises reacting an acyl halide with bis(2-aminophenyl)disulfide to acylate the amino groups of the bis(2-aminophenyl)disulfide in the presence of a base (e.g. N-methylmorpholine, di-N-methylpiperazine, or pyridine).

The starting materials, reagents and catalysts, which do not have their synthetic route explicitly disclosed herein, are generally available from commercial sources or are readily prepared using methods known to the person skilled in the art. For instance, the compounds of formulae (II) and (IV) can be prepared according to the procedures described in Shinkai et al., J. Med. Chem. 43:3566-3572 (2000), WO 2007/051714, or WO 2008/074677.

The preparation of the compound of formula (IV) comprises the preparation of a cyclohexanecarbonitrile derivative of formula (VI) followed by the hydrolysis steps as described hereunder and in the following scheme 4.

The compound of formula (VI) can be prepared by reacting compound of formula (VII):

with an alkylating agent such as 1-halo-2-ethylbutane, or 2-ethyl-1-butanol and a Grignard reagent, such as a (C₁-C₆)alkyl-magnesium-halide, phenyl-magnesium-halide, heteroaryl-magnesium-halide or a (C₃-C₆)cycloakyl-magnesium-halide. In particular, the above mentioned coupling reaction is carried out in the presence of a secondary amine. In particular, the Grignard reagent is added to the cyclohexanecarbonitrile, and more particularly in the presence of a secondary amine, followed by the addition of an alkylating agent, as defined above. In particular, the above mentioned coupling reaction is followed by a mineral acid quenching, such as hydrofluoric acid, hydrochloric acid, boric acid, acetic acid, formic acid, nitric acid, phosphoric acid or sulfuric acid, most particularly by hydrochloric acid.

The compound of formula (IV) can be prepared by the following steps:

a) hydrolysis of a cyclohexanecarbonitrile derivative of formula (VI):

with H₂O in the presence of a strong acid, or with an aqueous base, to obtain a cyclohexanecarboxylic acid amide derivative of formula (V):

b) react the cyclohexanecarboxylic acid amide derivative of formula (V) with a nitrosylating agent, to obtain the compound of formula (IV). The nitrosylating agent can be generated in situ e.g. mixing H₂SO₄ and nitrous acid (HNO₂) or H₂SO₃/HNO₃ or N₂O₃/H₂SO₄ or HNO₃/SO₂ to obtain nitrosulfuric acid (NOHSO₄).

In another embodiment, the present invention provides a composition comprising a compound of formula (I):

and comprising a compound of formula (V):

and having less than 0.1% of the compound of formula (V) by weight.

In another embodiment, the present invention provides a composition comprising a compound of formula (I):

comprising a compound of formula (V):

and having between 1 ppb (parts per billion in weight) and 100 ppm (parts per million in weight) of the compound of formula (V), and in particular embodiments having between 1 ppb and 1 ppm of the compound of formula (V).

In another embodiment, the present invention provides a composition comprising:

a compound of formula (I):

a compound of formula (X):

and a compound of formula (V)

wherein the composition has less than 0.1% of the compound of formula (X) by weight and less than 0.1% of the compound of formula (V) by weight.

In another embodiment, the present invention provides a composition comprising:

a compound of formula (I):

a compound of formula (X):

and a compound of formula (V):

and having between 1 ppb (parts per billion in weight) and 100 ppm (parts per million in weight) of the compound of formula (X) and between 1 ppb (parts per billion in weight) and 100 ppm (parts per million in weight) of the compound of formula (V), and in particular embodiments having between 1 ppb and 1 ppm of the compound of formula (X) and between 1 ppb and 1 ppm of the compound of formula (V).

In another embodiment, the invention provides a pharmaceutical composition comprising a compound of formula (I), also known as thioisobutyric acid S-(2-{[1-(2-ethyl-butyl)-cyclohexanecarbonyl]-amino}-phenyl) ester, S-[2-([[1-(2-ethylbutyl)-cyclohexyl]-carbonyl]amino)phenyl]2-methylpropanethioate or dalcetrapib, and a compound of formula (X). In particular, the composition comprises a compound of formula (I) and between 1 ppb and 100 ppm of a compound of formula (X), more particularly between 1 ppb and 1 ppm.

In another embodiment, the invention provides a pharmaceutical composition comprising a compound of formula (I) and a compound of formula (V). In particular, the composition comprises a compound of formula (I) and between 1 ppb and 100 ppm of a compound of formula (V), and more particularly between 1 ppb and 1 ppm.

In another embodiment, the invention provides a pharmaceutical composition comprising a compound of formula (I), a compound of formula (X) and a compound of formula (V). In particular embodiments, the composition comprises a compound of formula (I), between 1 ppb and 100 ppm of a compound of formula (X) and between 1 ppb and 100 ppm of a compound of formula (V).

In general, the nomenclature used herein is based on AUTONOM™ 2000, a Beilstein Institute computerized system for the generation of IUPAC systematic nomenclature. Chemical structures shown herein were prepared using MDL ISIS™ version 2.5 SP2. Any open valency appearing on a carbon, oxygen or nitrogen atom in the structures herein indicates the presence of a hydrogen atom.

The following examples are provided for the purpose of further illustration and are not intended to limit the scope of the claimed invention.

The following abbreviations and definitions are used: Ar (argon); acid chloride (1-(2-ethyl-butyl)-cyclohexanecarbonyl chloride); amidodisulfide (N,N′-(dithiodi-2,1-phenylene)bis[1-(2-ethylbutyl)-cyclohexanecarboxamide]); amidothiophenol (1-(2-ethylbutyl)-N-(2-mercaptophenyl)-cyclohexanecarboxamide); thioester (S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate); DTDA (2,2′-dithiodianiline); d.i. (deionized); eq. (equivalent); EtOH (ethanol); g (gram); HPLC (high-performance liquid chromatography); GC (gas chromatography); h (hour); M (Molarity [moles/L]); MeOH (methanol); ml (milliliter); and RT (room temperature).

The pressure indicated in the experiments is the gauge pressure, i.e. the pressure relative to the local atmospheric pressure.

Example 1 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

A solution of 8.2 g of amidodisulfide (12.9 mmol) in 16.9 g toluene and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave, which was sealed and 3 times pressurized with 5 bar H₂ and released to atmospheric pressure. The autoclave was heated under program control to 80° C., and thereafter charged with 5 bar of H₂. The hydrogenation was carried out under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). After this time the autoclave was cooled to RT, the pressure released and the reaction mixture filtered. The filtrate was evaporated under 50° C./15 mbar and dissolved in 78 g EtOH. Addition of 22 g d.i. H₂O under Ar at RT leads to the precipitation of 9.67 g thioester (yield 96.3%) as white crystals with a melting point of 64.2-64.4° C. The observed amount of 1-(2-ethylbutyl)-N-(2-mercaptophenyl)-cyclohexanecarboxamide was less than 0.5%.

Example 2 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 1 but using 12.8 g toluene. After work-up and crystallization, 9.63 g of thioester as white crystals (yield 96%) with 100% HPLC area % purity was isolated.

Example 3 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 1 but using 26.7 g toluene. After work-up and crystallization, 9.73 g of thioester as white crystals (yield 97%) with 100% HPLC area % purity was isolated.

Example 4 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g toluene and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. It was hydrogenated under vigorous stirring for 3 hrs at the temperature of 90° C. and 5 bar (0.5 MPa). Work-up according to example 1 afforded 9.63 g of thioester as white crystals (yield 95.9%). HPLC analysis showed a purity of 100 area %.

Example 5 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 1 but using 552 mg 20% Pd(OH)₂/C catalyst (519 μmol Pd, wet, ca. 50 weight % H₂O), which was washed 3 times first with THF and then 3 times with Toluene before being transferred in the autoclave. The mixture was hydrogenated under vigorous stirring for 5 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). After work-up according to example 1, 9.76 g of thioester as white crystals (yield 97.2%) were recovered. HPLC analysis showed a purity of 100 area %.

Example 6 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 1 but using 1.15 g 4.78% nPdnAl2O3/Al2O3 catalyst (519 μmol Pd, SDC materials). The mixture was hydrogenated under vigorous stirring for 5 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). Work-up according to example 1 afforded 9.86 g of thioester as white crystals (yield 98.2%). HPLC analysis showed a purity of 100 area %.

Example 7 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g toluene and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. It was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 0.2 bar (0.02 MPa). Work-up according to example 1 afforded 9.39 g of thioester as white crystals (yield 93.5%). HPLC analysis showed a purity of 100 area %.

Example 8 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g ethyl acetate and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. The mixture was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). HPLC analysis showed complete conversion. Work-up according to example 1 afforded 8.54 g of thioester as white crystals (yield 85.1%). HPLC analysis showed a purity of 100 area %.

Example 9 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 8 but using tert-butyl methyl ether. It was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). HPLC analysis showed complete conversion. Work-up according to example 1 afforded 8.89 g of thioester as white crystals (yield 88.5%). HPLC analysis showed a purity of 100 area %.

Example 10 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g toluene and 4.2 g (38.7 mmol) isobutyryl chloride was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. The mixture was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). Thereafter the reaction mixture was analyzed with HPLC, showed 70.6% conversion of amidodisulfide and 52% thioester HPLC area %. In addition 2.9 area % of 1-(2-ethylbutyl)-N-(2-mercaptophenyl)-cyclohexanecarboxamide and 14.5 area % of 2-[1-(2-ethyl-butyl)-cyclohexyl]-benzothiazole were formed.

Example 11 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

This example was run in an analogous manner to example 10 but using 2.0 eq. isobutyric anhydride (4.1 g, 25.8 mmol) as reagent. The mixture was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). HPLC analysis showed complete conversion. Work-up according to example 1 afforded 7.05 g of thioester as white crystals (yield 68.5%). HPLC analysis showed a purity of 100 area %.

Example 12 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 22.9 g isobutyric anhydride (145 mmol) was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. The mixture was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 5 bar (0.5 MPa). HPLC analysis showed complete conversion. Work-up according to example 1 afforded 9.57 g of thioester as white crystals (yield 95.3%). HPLC analysis showed a purity of 100 area %.

Example 13 1-(2-ethylbutyl)-N-(2-mercaptophenyl)-cyclohexanecarboxamide

8.2 g of amidodisulfide (12.9 mmol) in 22.9 g toluene was transferred together with 552 mg Pd/C (519 μmol Pd, EVONIK E101 N/D 10%) to a 185 mL stainless steel autoclave. It was hydrogenated under vigorous stirring for 18 hrs at the temperature of 80° C. and 10 bar (1.0 MPa). Thereafter the reaction mixture was analyzed with HPLC, showed 100% conversion of amidodisulfide and 99.2% amidothiophenol HPLC area %.

Example 14 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g toluene and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 327 mg Raney-Ni (2.59 mmol Ni, EVONIK B113 Z 46.5%) to a 185 mL stainless steel autoclave. It was hydrogenated under vigorous stirring for 18 hrs at the temperature of 100° C. and 1 bar (0.1 MPa). Thereafter the reaction mixture was analyzed with HPLC, showing 100% conversion of amidodisulfide and 100% thioester.

Example 15 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

8.2 g of amidodisulfide (12.9 mmol) in 16.8 g toluene and 6.1 g (38.7 mmol) isobutyric anhydride was transferred together with 1.35 g Nanoparticulate Palladium(0) microencapsulated in polyurea matrix (NP Pd(0) Encat™ 30, sold by Sigma-Aldrich®) (540 μmol Pd, 0.4 mmol Pd/g) to a 185 mL stainless steel autoclave. It was hydrogenated under vigorous stirring for 18 hrs at the temperature of 90° C. and 30 bar (3 MPa). Thereafter the reaction mixture was analyzed with HPLC, showed complete conversion of amidodisulfide and 100% desired product. This catalyst was reused under the same condition for further 10 times, all of them showed the same result i.e. complete conversion and 100% desired product.

Example 16 Synthesis of S-[2-[1-(2-ethylbutyl)cyclohexanecarbonylamino]-phenyl] 2-methylthiopropionate

In the table hereunder, the reactions were carried in analogous manner to example 1,

wherein the reaction conditions were: 0.314 mmol amidodisulfide in 410 mg toluene, 3 eq. isobutyric anhydride, 0.0403 eq. metal catalyst (specifically mentioned in the following table), 80° C., 5 bar, reaction time 18 hrs. Thereafter the reaction mixture was analyzed with HPLC.

Conversion Yield Catalysts HPLC [area %] HPLC [area %] 3% Au/TiO2 69 65 5% Ru/Al₂O₃ 81.1 71.8 5% Pt/C 99.0 73.0 5% Rh/C 87.0 73.0 93% Co_Al (~50% H2O) 49.0 43.0 5% Ir/CaCO3 70.0 65.5

Unless stated to the contrary, all compounds in the examples were prepared and characterized as described. All ranges recited herein encompass all combinations and subcombinations included within that range limit. All patents and publications cited herein are hereby incorporated by reference in their entirety. 

1. A process for the preparation of a compound of formula (I″):

wherein X¹, X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d)′ or —NR^(e) ₂; or alternatively two adjacent substituents selected from the group consisting of: (1) X¹ and X²; (2) X² and X³; and (3) X³ and X⁴, together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH and S, wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, a (C₃-C₈)cycloalkyl, aryl or heteroaryl; and each R^(e) is independently hydrogen, a (C₁-C₈)alkyl, or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′), X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d), or —NR^(e) ₂; or alternatively, two adjacent substituents selected from the group consisting of: (1) X¹ and X²; (2) X² and X³; and (3) X³ and X⁴, together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH and S, wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined above, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 2. A process for the preparation of a compound of formula (I″):

wherein X¹, X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or alternatively, two adjacent substituents selected from the group consisting of: (1) X¹ and X²; (2) X² and X³; and (3) X³ and X⁴, together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH and S, wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; R¹ is a (C₁-C₈)alkyl or aryl; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, a (C₃-C₈)cycloalkyl, aryl or heteroaryl; and each R^(e) is independently hydrogen, a (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′), X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; or alternatively, two adjacent substituents selected from the group consisting of: (1) X¹ and X²; (2) X² and X³; and (3) X³ and X⁴, together with the carbon atoms to which they are attached form a four, five or six membered cycloalkyl ring that optionally includes an additional heteroatom selected from the group consisting of O, NH and S, wherein the four, five or six membered cycloalkyl ring is optionally substituted with one to three substituents independently selected from the group consisting of a (C₁-C₈)alkyl and aryl; and wherein R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined above, with H₂ in the presence of (1) an acylating agent or a halide derivative and (2) a heterogeneous transition metal hydrogenation catalyst.
 3. The process according to claim 1, wherein X¹ is —NH—C(═O)R^(d) and R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl; X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; which comprises reacting a compound of formula (II″):

wherein X^(1′) is —NH—C(═O)R^(d) or —NR^(e′) ₂; R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl; R^(e′) is hydrogen; X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined in claim 1, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 4. The process according to claim 2, wherein X¹ is —NH—C(═O)R^(d), and R^(d) is a (C₃-C₈)cycloalkyl substituted by (C₁-C₈)alkyl; X², X³ and X⁴ are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d) or —NR^(e) ₂; R^(a), R^(b), R^(c) and R^(d) are independently a (C₁-C₈)alkyl, a (C₃-C₈)cycloalkyl, aryl or heteroaryl; each R^(e) is independently hydrogen, a (C₁-C₈)alkyl or aryl; and R¹ is a (C₁-C₈)alkyl or aryl; which comprises reacting a compound of formula (II″):

wherein X^(1′) is —NH—C(═O)R^(d) or —NR^(e′) ₂; R^(d) is a (C₃-C₈)cycloalkyl substituted by a (C₁-C₈)alkyl; R^(e′) is hydrogen; X^(2′), X^(3′) and X^(4′) are each independently hydrogen, a (C₁-C₈)alkyl, aryl, heteroaryl, —OR^(a), —O—C(═O)R^(b), —NHR^(c), —NH—C(═O)R^(d), or —NR^(e) ₂; and R^(a), R^(b), R^(c), R^(d), R^(e), X¹, X², X³ and X⁴ are as defined in claim 2, with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 5. The process according to claim 1, wherein R^(d) is (2-Ethyl-butyl)-cyclohexyl.
 6. The process according to claim 1, wherein X², X³ and X⁴ are each independently hydrogen or a (C₁-C₈)alkyl.
 7. The process according to claim 1, wherein X^(2′), X^(3′) and X^(4′) are each independently hydrogen or a (C₁-C₈)alkyl.
 8. The process according to claim 1, for the preparation of a compound of formula (I′):

which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 9. The process according to claim 1, for the preparation of a compound of formula (I′) and formula (X):

which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 10. The process according to claim 2 for the preparation of a compound of formula (Ia):

wherein R¹ is a (C₁-C₈)alkyl or aryl, which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of (1) an acylating agent or halide derivative and (2) a heterogeneous transition metal hydrogenation catalyst.
 11. The process according claim 2 for the preparation of compounds of formula (Ia) and Formula (X):

wherein R¹ is a (C₁-C₈)alkyl or aryl, which comprises reacting a compound of formula (II′):

wherein R is H or a compound of the formula:

with H₂ in the presence of (1) an acylating agent or a halide derivative and (2) a heterogeneous transition metal hydrogenation catalyst.
 12. The process according to claim 11, wherein R is:


13. The process according to claim 2 wherein R¹ is isopropyl and the acylating agent is isobutyric anhydride or isobutyryl halide.
 14. The process according to claim 2 wherein the acylating agent is isobutyric anhydride.
 15. The process according to claim 14, wherein 2.0 to 4.0 equivalents of isobutyric anhydride with respect to the disulfide of formula (II) is used.
 16. The process according to claim 1 in the presence of a solvent or a mixture of two or more solvents.
 17. The process according to claim 16, wherein the solvent is an organic solvent.
 18. The process according to claim 16, wherein the solvent is an ether like solvent, ester like solvent, aliphatic hydrocarbon solvent, saturated alicyclic hydrocarbon solvent, aromatic solvent or a mixture thereof.
 19. The process according to claim 16, wherein the solvent is an aliphatic hydrocarbon solvent, saturated alicyclic hydrocarbon solvent, or aromatic solvent.
 20. The process according to claim 2 wherein the acylating agent is an anhydride derivative which can act as a solvent or co-solvent with a molar ratio anhydride/amidodisulfide of 2 to
 19. 21. A process for the preparation of S-[2-([[1-(2-ethylbutyl)-cyclohexyl]-carbonyl]amino)phenyl]2-methylpropanethioate comprising the formation of a compound of formula (I′):

which comprises reacting compound of formula (II):

with H₂ in the presence of a heterogeneous transition metal hydrogenation catalyst.
 22. The process according to claim 21, wherein the H₂ is added at a pressure of at least 0.1 bar.
 23. The process according to claim 1, wherein the reaction is carried out at temperature up to 150° C.
 24. The process according to claim 1, wherein the heterogeneous transition metal hydrogenation catalyst is a Raney catalyst, Pd/C, Pd(OH)₂/C, Nanoparticulate Palladium(0) microencapsulated in polyurea matrix, Au/TiO₂, Rh/C, Ru/Al₂O₃, Ir/CaCO₃, Pt/C, or a mixture thereof.
 25. The process according to claim 1, wherein the heterogeneous transition metal hydrogenation catalyst is a Raney catalyst, Pd/C, Pd(OH)₂/C, Au/TiO₂, Rh/C, Ru/Al₂O₃, Ir/CaCO₃, Pt/C, or a mixture thereof.
 26. The process according to claim 1, wherein the heterogeneous transition metal hydrogenation catalyst is Pd/C, Pd(OH)₂/C, Au/TiO₂, Rh/C, Ra—Ni or Pt/C.
 27. The process according to claim 1, wherein the heterogeneous transition metal hydrogenation catalyst is Pd/C or Ra—Ni.
 28. (canceled)
 29. (canceled)
 30. (canceled)
 31. A composition comprising a compound of formula (I):

and a compound of formula (V):

which has less than 0.1% of the compound of formula (V) by weight.
 32. A composition according to claim 31 having between 1 ppb and 100 ppm of the compound of formula (V).
 33. (canceled)
 34. (canceled)
 35. (canceled)
 36. (canceled)
 37. A pharmaceutical composition comprising S-[2-([[1-(2-ethylbutyl)-cyclohexyl]-carbonyl]amino)phenyl]2-methylpropanethioate and a compound of formula (V).
 38. The pharmaceutical composition according to claim 37, wherein the composition comprises between 1 ppb and 100 ppm of the compound of formula (V).
 39. The pharmaceutical composition according to claim 36, wherein the pharmaceutical composition further comprises a compound of formula (V).
 40. The pharmaceutical composition according to claims 39 which comprises between 1 ppb and 100 ppm of the compound of formula (V). 